FIG. 4 is a block diagram showing the schematic arrangement of a radiographic imaging system including a conventional radiographic imaging apparatus. FIG. 5 is a schematic circuit diagram of an imaging means used in conventional radiographic imaging apparatus. FIG. 6 is a timing chart showing the driving timing for a conventional radiographic imaging apparatus.
As shown in FIG. 4, a conventional radiographic imaging system 400 includes a radiation generator 401, an imaging means 402, a radiation I/F 403, and a control means 404 (see, for example, Japanese Patent Laid-Open No. 08-130682 and U.S. Pat. Nos. 5,677,940 and 6,515,286). The imaging means 402 is connected to the control means 404 via cable 405c. Control signals such as driving pulses are supplied from the control means 404 to the imaging means 402. The radiation generator 401 and the control means 404 are connected to each other through the radiation I/F 403. The radiation generator 401 and the radiation I/F 403 are connected to each other via the cable 405b. The radiation I/F 403 and control means 404 are connected to each other via the cable 405a. 
As shown in FIG. 5, the imaging means 402 used in conventional radiographic imaging apparatus has an area sensor 501 performing matrix driving, which has a two-dimensional array of pixels each comprising a photoelectric conversion element such as a p-i-n photodiode formed by using amorphous-silicon and a switching element such as a thin-film transistor (TFT) (see, for example, U.S. Pat. No. 5,079,426). A bias voltage Vs is applied from a power supply to the common electrode side of the p-i-n photodiode of each pixel. The gate electrode of the TFT of each pixel is connected to a corresponding one of the common gate lines Vg1 to Vg3. The common gate lines are connected to a gate driver 502 comprising shift registers and the like (not shown). The source electrode of each TFT is connected to a corresponding one of the common data lines Sig1 to Sig3. A reading unit 503 which outputs an image signal comprises input amplifiers 504, sample and hold circuits 505, an analog multiplexer 506, an output amplifier 507, and the like.
The operation of the conventional radiographic imaging system 400 will be described next with reference to the timing chart of FIG. 6. Referring to FIG. 6, signals RES, Vg1, Vg2, Vg3, and SMPL are control signals to be supplied from the control means 404 to the imaging means 402 in FIG. 4. These signals are also shown in FIG. 5. In this case, the signal RES is used to reset the common data lines and the input amplifiers 504, the signals Vg1 to Vg3 are applied to the gates of the TFTs connected to the respective common gate lines, and the signal SMPL is used to transfer charges to the capacitors of the sample and hold circuits 505. An analog output is an output signal which is output from the reading unit 503 and contains the information of an object.
The conventional radiographic imaging system 400 supplies control signals to the radiation generator 401 and imaging means 402 by using the common control means 404 to make the radiation generator 401 and imaging means 402 operate synchronously. This makes it possible to synchronize a radiation control signal A supplied from the control means 404 to the radiation I/F 403 with a radiation control signal C supplied from the control means 404 to the imaging means 402.
However, since a device such as a relay is used for the radiation I/F 403, a timing delay occurs. For this reason, in some case, the radiation control signal A is supplied, as a radiation control signal B obtained by delaying the signal A by a predetermined interval (e.g., an interval D in FIG. 6), to the radiation generator 401. In this case, the radiation generator 401 generates pulse-like radiation to the imaging means 402 in accordance with the radiation control signal B obtained by delaying the radiation control signal A by a predetermined interval.
In radiographic imaging system based on pulse radiation emissions, radiation emissions can be inhibited during read intervals A-B and A′-B′ of FIG. 6. For this reason, the control means 404 needs to supply the control signals RES, Vg1, Vg2, Vg3, and SMPL and the like to the imaging means 402 upon setting a timing margin in consideration of the delay of the above radiation pulse and the like.
In addition, the relay device used for the radiation I/F has a large delay and is unstable, and hence it is difficult to perform accurate timing control. That is, a timing limitation tends to occur. Because of this limitation, high-speed reading is inevitably required. As a consequence, some disadvantageous effects may occur in terms of the noise band.
Also available is a method of image capturing by irradiating an object with continuous radiation without synchronizing the radiographic imaging apparatus with the imaging means. In this method, however, an image of a moving object blurs and this results in a deterioration of the image quality.